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Stable Habitats (stable + habitat)
Selected AbstractsRelating streamflow characteristics to specialized insectivores in the Tennessee River Valley: a regional approach,ECOHYDROLOGY, Issue 4 2008Rodney R. Knight Abstract Analysis of hydrologic time series and fish community data across the Tennessee River Valley identified three hydrologic metrics essential to habitat suitability and food availability for insectivorous fish communities in streams of the Tennessee River Valley: constancy (flow stability or temporal invariance), frequency of moderate flooding (frequency of habitat disturbance), and rate of streamflow recession. Initial datasets included 1100 fish community sites and 300 streamgages. Reduction of these datasets to sites with coexisting data yielded 33 sites with streamflow and fish community data for analysis. Identification of critical hydrologic metrics was completed using a multivariate correlation procedure that maximizes the rank correlation between the hydrologic metrics and fish community resemblance matrices. Quantile regression was used to define thresholds of potential ranges of insectivore scores for given values of the hydrologic metrics. Increased values of constancy and insectivore scores were positively correlated. Constancy of streamflow maintains wetted perimeter, which is important for providing habitat for fish spawning and increased surface area for invertebrate colonization and reproduction. Site scores for insectivorous fish increased as the frequency of moderate flooding (3 times the median annual streamflow) decreased, suggesting that insectivorous fish communities respond positively to less frequent disturbance and a more stable habitat. Increased streamflow recession rates were associated with decreased insectivore scores. Increased streamflow recession can strand fish in pools and other areas that are disconnected from flowing water and remove invertebrates as food sources that were suspended during high-streamflow events. Copyright © 2008 John Wiley & Sons, Ltd. [source] Temporal patterns of geographic parthenogenesis in a freshwater snailBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2007FRIDA BEN-AMI Geographic parthenogenesis describes the observation that parthenogenetic organisms tend to occupy environments different from those of their close, sexually reproducing relatives. These environments are often described as extreme or disturbed habitats. We examined whether patterns of geographical parthenogenesis persist over time, by conducting a 3-year life-history survey and comparing two very proximate habitats of the freshwater snail Melanoides tuberculata: Nahal Arugot, a desert stream naturally disturbed by flash floods, and Or Ilan, a stable freshwater pond. Both sites occur in a xeric environment and are subject to otherwise similar biotic (e.g. parasites, predators) and climatic conditions. In the stable habitat, male frequencies and snail densities were significantly higher than in the disturbed one, whereas infection levels, mean embryo counts, and water temperatures were similar at both sites. Additionally, male frequencies declined after density decreased, thereby providing evidence for geographical parthenogenesis via reproductive assurance. Infection prevalence was very low regardless of reproduction mode. Although further genetic work is required, the apparent metapopulation structure of M. tuberculata in the Judean desert may be suitable for evaluating other possible explanations of geographical parthenogenesis. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 91, 711,718. [source] Microbiotic crusts as biomarkers for surface stability and wetness duration in the Negev DesertEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2009Giora J. Kidron Abstract Microbiotic crusts play an important role in arid and semi-arid regions. Yet, very little information exists regarding the factors that impact their development. In an attempt to assess the main factors that may determine their growth, measurements of the amount of fines (silt and clay), rain, moisture content, wetness duration and wind erosion and deposition were carried out along a 12 station transect within a partially crusted dune field in the western Negev Desert and compared to the crust cover and chlorophyll content. Surface stability was the only variable that exhibited significant relationship with crust cover while daylight wetness duration exhibited strong positive relationship (r2 = 0·92,0·99) with the crust's chlorophyll content. The data point out that microbiotic crusts may serve as a useful biomarker for surface stability. While wetness duration and wind will control crust cover and the crust chlorophyll content in semi-stable habitats (with absolute annual change in sand level of 2,3 mm), stable habitats (absolute change <1 mm) will be controlled primarily by moisture, while habitats with low surface stability (absolute change of tens and hundreds of millimeters) will be primarily controlled by wind. Furthermore, owing to the strong positive relationship between daylight wetness duration and the crust's chlorophyll content, the crust may serve as a useful biomarker for the quantification of surface wetness duration. Copyright © 2009 John Wiley & Sons, Ltd. [source] Sexual conflicts, loss of flight, and fitness gains in locomotion of polymorphic water stridersENTOMOLOGIA EXPERIMENTALIS ET APPLICATA, Issue 3 2007Pablo Perez Goodwyn Abstract In insect wing polymorphism, morphs with fully developed, intermediate, and without wings are recognized. The morphs are interpreted as a trade-off between flight and flightlessness; the benefits of flight are counterbalanced by the costs of development and the maintenance of wings and flight muscles. Such a trade-off has been widely shown for reproductive and developmental parameters, and wing reduction is associated with species of stable habitats. However, in this context, the role of water locomotion performance has not been well explored. We chose seven water striders (Heteroptera: Gerridae) as a model to study this trade-off and its relation to sexual conflicts, namely, Aquarius elongatus (Uhler), Aquarius paludum (Fabr.), Gerris insularis (Motschulsky), Gerris nepalensis Distant, Gerris latiabdominis Miyamoto, Metrocoris histrio (White), and Rhagadotarsus kraepelini Breddin. We estimated the locomotion performance as the legs' stroke force, measured on tethered specimens placed on water with a force transducer attached to their backs. By dividing force by body weight, we made performance comparisons. We found a positive relationship between weight and force, and a negative one between weight and the force-to-weight ratio among species. The trade-off between water and flight locomotion was manifested as differences in performance in terms of the force/weight ratio. However, the bias toward winged or wing-reduced morphs was species dependent, and presumably related to habitat preference. Water strider species favouring a permanent habitat (G. nepalensis) showed higher performance in the apterous morph, but in those favouring temporary habitats (A. paludum and R. kraepelini) morphs' performance did not differ significantly. Males had higher performance than females in all but three species studied (namely, A. elongatus, G. nepalensis, and R. kraepelini); these three have a type II mating strategy with minimized mating struggle. We hypothesized that in type I mating system, in which males must struggle strongly to subdue the female, males should outperform females to copulate successfully. This was not necessarily true among males of species with type II mating. [source] Biodiversity and resource use of larval chironomids in relation to environmental factors in a large riverFRESHWATER BIOLOGY, Issue 6 2002CHRISTIAN FESL 1.,Larval chironomids were examined at four sites on a cross-section of the River Danube in Austria between September 1995 and August 1996. The sites differed in hydraulics, sediment composition and habitat stability. 2.,Species,accumulation curves, showing the increase in number of species with increasing sampling effort, from three main channel sites were best described by a logarithmic model, suggesting that most of the species occurring at these sites were found. Data from a site connected to a backwater fitted best to a power model, indicating a random assemblage with additional species immigrating from the backwater area. 3.,Properties of the community were estimated using Jackknife techniques: species richness (range of mean values at the four sites: 32,91), H, diversity (1.5,2.3), evenness (0.23,0.28), spatial resource width (0.01,0.06), spatial resource overlap (0.13,0.20), spatial species aggregation (0.60,0.77), temporal community persistence (Kendal's correlation coefficient: 0.47,0.60) and beta-diversity (6.2,9.7). 4.,Redundancy analysis (RDA) was used to relate the community properties and species abundance to environmental factors. Habitat stability was the major factor associated with community structure. Higher sediment turnover led to higher spatial aggregation and, consequently, a decrease in spatial resource width and overlap, and to a decline in larval density and species richness. 5.,Species-abundance patterns agreed well with the log-normal model. Moderate community persistence and stability of the streambed sediments suggest that the log-normal model may be a good descriptor for communities of intermediately disturbed habitats, like large rivers, rather than stable habitats. [source] Parallel habitat-driven differences in the phylogeographical structure of two independent lineages of Mediterranean saline water beetlesMOLECULAR ECOLOGY, Issue 18 2009P. ABELLÁN Abstract It has been hypothesized that species living in small lentic water bodies, because of the short-term geological persistence of their habitat, should show higher dispersal ability, with increased gene flow among populations and a less pronounced phylogeographical structure. Conversely, lotic species, living in more geologically stable habitats, should show reduced dispersal and an increased phylogeographical structure at the same geographical scales. In this work we tested the influence of habitat type in two groups of aquatic Coleoptera (Nebrioporus ceresyi and Ochthebius notabilis groups, families Dytiscidae and Hydraenidae respectively), each of them with closely related species typical of lotic and lentic saline Western Mediterranean water bodies. We used mitochondrial cox1 sequence data of 453 specimens of 77 populations through the range of nine species to compare a lotic vs. a lentic lineage in each of the two groups. Despite the differences in biology (predators vs. detritivorous) and evolutionary history, in both lotic lineages there was a higher proportion of nucleotide diversity among than within groups of populations, and a faster rate of accumulation of haplotype diversity (as measured by rarefaction curves) than in the lentic lineages. Similarly, lotic lineages had a higher absolute phylogenetic diversity, more remarkable considering their smaller absolute geographical ranges. By comparing closely related species, we were able to show the effect of contrasting habitat preferences in two different groups, in agreement with predictions derived from habitat stability. [source] | |||||||||||||